The present invention relates to a keyboard assembly for providing electrical outputs corresponding to multiple keys, to signal utilization electronic devices such as typewriters and other data processing equipment.
In such a keyboard for electronic devices, a multiplicity of keys are disposed in plural rows to provide electric signals corresponding to the keys which have been depressed on their top faces. To improve ease of operation of the keys, attempts based on human engineering or ergonomics have been made to arrange the keys such that an operating surface generally defined by the top faces of the individual keys is curved to a downwardly convex shape in cross section across the rows of the keys. There have been proposed the following two methods to obtain such a curved operating surface of the keyboard:
The first method uses a curved key holder plate 2 having multiple guide holes 1, as shown in FIG. 1. The holder plate 2 is made from a steel plate by shaping it to a suitable curvature in the transverse cross section. In the guide holes 1, keystem guides 5 are fixedly inserted to slidably guide respective keystems 4 which carry at their upper ends keytops 3 having the finger-pressed top faces. In this case, the keys 3, 4 are all equally sized so that an operating surface 6 defined by the top faces is curved substantially to the curvature of the key holder plate 2.
In this method, however, it is required to fix the individual keystem guides 5 in the guide holes 1 formed in the shaped key holder plate 2. This assembling procedure is cumbersome and time-consuming, and reduces the efficiency of manufacture of the keyboard to an appreciable extent, and accordingly pushes up the cost of manufacture.
While the above method is advantageous in that the key holder plate 2, which is shaped under plastic working from a metal sheet, is capable of maintaining an initially given curved profile virtually permanently, the metal plate is required to be relatively thick for permanency of the original shape, and this inherently increases a total weight of the keyboard assembly, which may be considered as an undesired factor in the recent trend in the art toward providing compact and lightweight equipment.
The second method is illustrated in FIG. 2, wherein an upper casing 7 of a keyboard is provided with integrally formed keystem guides 8 which slidably support respective keystems 9 having keytops 10 fixed to their upper ends. In this method, an operating surface 11 of the keyboard is established by forming the keytops 10 in different sizes and shapes, depending upon the positions in which they are disposed. For example, the keytops 10 carried on the keystems 9 disposed in one of plural rows are formed with a top face having a curvature which is different from that of the keytops 10 carried on the keystems 9 in another of the plural rows.
Thus, the above second known method requires different kinds of keytops or keytops and keystems to provide different contours of top faces of the keys so that the top faces cooperate to form the curved operating surface 11. This means a need of using different kinds of molds for forming the different keys, and consequently an increased cost of manufacture of the keyboard assembly.